1. Field of Invention
The present invention relates to a power converter, and particularly to a DC/DC power converter with boosting, bucking and charging functions.
2. Description of the Related Art
A power converter is used for converting an input power supply voltage to one or more output voltages in many modes. “Switch mode” power converter have several types, for example, a boost power converter and a buck power converter.
With a low-power product application, switch mode power converter works either in boost mode or in buck mode. In boost mode, a voltage is boosted to a higher one; on the contrary, in buck mode, a voltage is bucked to a lower one.
In portable/handheld electronic products for example, the operation voltage of an internal circuit thereof is between 1.8V-2.5V. Therefore, for a Li-Ion battery (Lithium-Ion battery) used as a power supply, the power converter is operated in buck mode for reducing the power voltage of 4.2V-3.0V to a voltage of 2.8V-2.5V. On the other hand, for a 1.5V dry battery used as a power supply, the power converter is operated in boost mode for increasing the power voltage of 1.5V to a voltage of 1.8V-2.5V.
Referring to FIG. 1, it is a schematic block diagram showing a conventional switch mode power converter 10 with an inductor-based boost/buck circuit. The power circuit 10 includes a boost/buck timing control module (TCM) 15, an inductor L1, transistors M1 and M2 and switches S1-S4.
A battery 12 in FIG. 1 can be, for example, a NiMH battery (Nickel-Metal-Hydride battery), a NiCd battery (Nickel-Cadmium battery), a Li-Ion battery (Lithium-Ion battery) or a Li-polymer battery. Vb indicates the voltage of battery 12, herein.
According to a boost/buck selection signal CS, the boost/buck TCM 15 turns on or turn off the transistors M1 and M2, and the switches S1-S4, which dominates the power converter to be operated in boost mode or in buck mode. As the battery voltage Vb is higher than a required output voltage Vo, the power converter 10 is in buck mode to convert the voltage Vb into a lower output voltage Vo. While the battery voltage Vb is lower than a required output voltage Vo, the power converter 10 is in boost mode to convert the voltage Vb into a higher output voltage Vo.
In portable electronic products utilizing a rechargeable battery as the power supply thereof, a charger is needed to charge the rechargeable battery.
Referring to FIG. 2, it is a schematic block diagram showing a conventional charger 20 for charging a rechargeable battery 26. The charger 20 includes an external power supply 21, a battery status detection and charge-control module 23, an inductor L2 and transistors M3 and M4.
The external power supply 21 can be a power adaptor for converting AC into DC. An increasingly used external power supply for many handheld electronic products is a USB (universal serial bus) socket today. A handheld electronic product is just simply plugged in an USB socket on a computer for charging.
The battery status detection and charge-control module 23 is used for detecting electric energy status of the rechargeable battery 26 or the voltage Vb and providing a control signal to the transistors M3 and M4. Usually, an external power voltage Vex is higher than the rechargeable battery voltage Vb. Accordingly, the charger is in buck mode to provide the rechargeable battery 26 with a voltage required by charging. Moreover, as the rechargeable battery 26 is fully energized, the battery status detection and charge-control module 23 would turn off the transistor M3 to avoid an excessive charge, which may damage the rechargeable battery 26.
In the prior art, a power converter and a charger are two independent circuits, that is, the power converter is built in an independent IC (integrated circuit) and the charger in another independent IC.
Such circuit layouts with a power converter and a charger independently on each other have a simpler design advantage although, but it results in an increased circuit size and a high cost.